1. Field of the Invention
The present invention relates to a method and apparatus for manufacturing a liquid crystal display device, and more particularly, to a method and apparatus for manufacturing a liquid crystal display device by using a liquid crystal dropping method.
2. Discussion of the Related Art
With rapid development of an information-oriented society, a need for an information display device having characteristics such as good image quality, light weight, small thickness, and low power consumption has correspondingly been increased. To meet this need, there has been much research directed toward various flat panel display device technologies, such as liquid crystal display device (LCD) technology, plasma display panel (PDP) technology, electro luminescent display (ELD) technology, vacuum fluorescent display (VFD) technology. Some of these display device technologies have already been applied in various applications as the information display device.
Of above various flat panel display devices, the LCD is currently the most widely used due to its ability to meet the above need. In fact, in portable devices such as notebook PC computers, LCD technology has replaced cathode ray tube (CRT) technology. Moreover, even in desktop type displays such as PC monitors and TV monitors, LCD technology has been developed and employed.
A liquid crystal cell includes two opposing substrates and a liquid crystal material filled between the substrates. Liquid crystal is a phase of material having intermediate properties between the liquid and the solid such as fluidity of liquids but long-range order of solids. The liquid crystal material, in an intermediate state between the liquid and the solid, has an optical anisotropy due to its long-range orientational order as well as mechanical fluidity. An LCD is manufactured through a number of processes such as an array process, a color filter process, a liquid crystal cell process, and a module process.
An array process is a process repeating a deposition, a photolithography, and an etching to form a thin film transistor (TFT) array on a first substrate (TFT substrate). A color filter process is a process for forming an ITO (Indium Tin Oxide) film for a common electrode, after red, green, and blue color filters (CF) of dyes or pigments are formed on a second substrate (CF substrate) having a black matrix formed thereon.
A liquid crystal cell process is a process of assembling the TFT substrate and the CF substrate prepared by the array process and the color filter process, respectively. Generally, an empty liquid crystal cell is formed with a fixed and thin gap between the first substrate and the second substrate. Then, the liquid crystal is filled through an opening around the gap to form a liquid crystal panel. A module process is a process for assembling a driving circuit part for processing input and output signals, connecting the liquid crystal panel to a signal processor, and assembling some frames, thereby completing the liquid crystal module.
The step of filling liquid crystal into the liquid crystal cell in the liquid crystal cell process step can be explained as follows.
In the liquid crystal filling step, a liquid crystal material is contained in a container disposed in a chamber. The chamber is maintained in a vacuum state for removing moisture and air dissolved in the liquid crystal material or contained inside the container. While maintaining the vacuum state of the chamber, a liquid crystal filling hole in the empty liquid crystal cell is dipped in the container, and brought into contact with the liquid crystal material. Then, the chamber is vented from a higher vacuum state to a lower vacuum state, and eventually to the atmospheric pressure state. Accordingly, the liquid crystal material is filled into the empty liquid crystal cell through the liquid crystal filling hole by a pressure difference between a pressure in the liquid crystal cell and a pressure in the chamber.
However, the above described liquid crystal filling method has poor productivity because the method needs long time for the liquid crystal filling. That is, before the liquid crystal material is filled into the liquid crystal cell, the large assembled panel must be cut into unit panels, a portion of the unit panel must be dipped into the container, and the liquid crystal filling hole must be brought into contact with the liquid crystal material while the chamber is kept at a vacuum state. Moreover, a large sized LCD is likely to have some defects coming from imperfect filling of the liquid crystal material into the cell.
With regard to this, a liquid crystal dropping method has been developed in which a fixed amount of the liquid crystal is dropped onto an inner surface of the TFT substrate in a corresponding area on the TFT substrate inside a main sealing area formed around the CF substrate (or, alternatively, TFT substrate). Then, the TFT substrate and the CF substrate are assembled into a large liquid crystal panel in a vacuum chamber. The liquid crystal cell process using the liquid crystal dropping method can be explained as follows.
Referring to FIG. 1, an orientation step (1S) in which an orientation material is coated on the TFT substrate and the CF substrate, and mechanical rubbing is carried out on the both substrates for having molecules of the liquid crystal material oriented, carried out. Then, the TFT substrate and the color filter substrate are cleaned (2S).
The TFT substrate includes a plurality of gate lines running in one direction at fixed intervals, and a plurality of data lines running in a direction perpendicular to the gate lines at fixed intervals. A plurality of thin film transistors and pixel electrodes are formed in a matrix pixel region defined by the gate lines and the data lines. The CF substrate includes a black matrix layer, a color filter, and a common electrode. Hence, the black matrix layer shields a light leakage of parts except the pixel region.
Then, the cleaned CF substrate is loaded onto a stage of a seal dispenser, and a sealing material is coated on a periphery of the panel (3S). The sealing material may be a photo-sensitive resin, or thermo-curing resin. Meanwhile, no filling hole or sealing structure for filling the cell with liquid crystal is required.
At the same time, the cleaned TFT substrate is loaded onto a stage of a silver (Ag) dispenser, and a silver paste material is dotted (i.e., dispensed) into a common voltage supply line of the TFT substrate (5S). Then, the TFT substrate is transferred to an LC dispenser, and liquid crystal material is dropped (i.e., dispensed) onto an active array region of each unit panel areas (6S). The liquid crystal dropping process is carried out as follows.
After a liquid crystal material is filled into an LC syringe before the LC syringe is assembled and set in the production line, moisture and air dissolved in the liquid crystal material is removed under a vacuum state (7S). Then, the liquid crystal syringe is assembled and set (8S), and mounted on the liquid crystal dispenser (9S). When the TFT substrate is loaded onto a stage of the liquid crystal dispenser, the liquid crystal material is dropped therefrom using the liquid crystal syringe (6S) by dotting a fixed amount of the liquid crystal material onto the TFT substrate at a predetermined pitch inside a coating area of the sealing material (i.e., the pixel region).
After the TFT substrate and the CF substrate are loaded into a vacuum assembling chamber, the TFT substrate and the CF substrate are assembled such that the dropped liquid crystal is uniformly spread over unit panel areas (10S). Then, the sealing material is cured (10S). The assembled TFT substrate and color filter substrate, that is, a large panel, is cut into individual unit panels (11S). Each unit panel is ground and inspected (12S), thereby completing the LCD unit panel.
However, the above method for manufacturing a liquid crystal display having the liquid crystal dropping method applied thereto has the following problems. In the above the liquid crystal cell process, after the orientation steps and the cleaning step, the formation step of silver dots, and the dispensing step of the liquid crystal material on the TFT substrate process, and the sealing material coating step on the CF substrate are carried out using two separate and parallel production lines until the vacuum assembling and curing step (10S). That is, two production lines are used so that the TFT substrate and the CF substrate respectively pass through the orientation step (1S), the cleaning step (2S), the sealing material coating step (3S), the silver dotting step (5S), and the liquid crystal dropping step (6S) in parallel production lines. The use of two production lines results in poor spatial efficiency, higher costs caused by two sets of expensive equipment, and efficiency losses due to different processing times between the two production lines (i.e., line unbalance). Moreover, an inoperative state of one production line caused by failure of the other line reduces productivity substantially.